I. Nm23. The PI discovered the first metastasis suppressor gene, Nm23. Basic and translational research has investigated the role of Nm23 in the regulation of tumor metastasis. Eleven transfection studies have documented that overexpression of Nm23 in various tumor cell lines resulted in a 50-90% decrease in tumor metastatic potential in vivo. The mechanism of Nm23 suppression of metastasis is likely complex. II. LPAR1 studies. One of the potential avenues to drug a suppressor gene is to identify inverse correlates of its expression. The lysophosphatidic acid receptor (LPA1, LPAR1), a G-protein coupled receptor for the serum lysophosphatidic acid (LPA) was found to be inversely related to Nm23 expression in cell lines, human breast tumors, and knock-out animal tissues. Forced re-expression of LPA1 overcame Nm23 suppression of tumor cell motility in vitro and metastasis in vivo. We hypothesized that an inhibitor of LPA1 would act as a metastasis suppressor and have preclinically validated Debio 0719. Administration of 0719 to animals injected into the mammary fat pad with murine 4T1 cells had no effect on primary tumor size. After surgical removal of the primary tumor, metastasis in the lymph nodes, lungs and liver was quantified 10 weeks post-injection. 0719 induced a significant suppression of metastasis in all sites. Other 4T1 experiments demonstrated that shRNA down-regulation of LPA1 also prevented metastasis, and is the mechanism of action of 0719. Treatment with 0719 only after mammary fat pad removal, akin to adjuvant therapy, was also metastasis suppressive. Confirmatory experiments showed a non-significant effect of 0719 on MDA-MB-231T human breast tumor growth in the mammary fat pad, but a significant inhibition of lung colonization after tail vein injection. When animals injected with MDA-MB-231T cells were treated with 0719 and the drug was removed, death ensued. Analysis of tissue from vehicle and 0719 treated animals showed that: (1) proliferation measured by Ki67 staining was high and equivalent in primary tumors treated with vehicle or 0719, but was reduced in lung and liver metastases treated with 0719; (2) similar trends were observed in pErk staining. The data indicate that 0719 induced site specific dormancy in metastasis, a novel indication for a drug to date. An M-CRADA was completed with Sanofi to use their SAR100842 compound, an orally available LPAR1 inhibitor under clinical testing for fibrosis. Seven in vivo experiments in breast and ovarian cancer were negative for metastasis suppression. Concurrently the compound failed in a trial for systemic sclerosis and the project dropped by the manufacturer. Following the fibrosis lead, we tested two recently FDA approved compounds for idiopathic pulmonary fibrosis, nintenadine and perfiridone, both of which were inactive. The mechansim of action of both fibrosis drugs is unknown. Current efforts are testing an orally available LPAR1 inhibitor from Epigen. This compound has not been in the clinic. Additional efforts are underway to obtain additional LPAR1 inhibitors that are orally available, and hopefully through Phase I clinical testing. III. The mechanism of Nm23 suppression of metastasis is likely multi-factorial. Nm23 has been reported to be a histidine protein kinase but the contribution of this function has been impossible to determine, as histidine is destroyed under acidic and heat conditions used for simple SDS-PAGE. Based on a recent publication of a phospho-histidine antibody, we have confirmed that Nm23 autophosphorylates on his 118, and are investigating the role of phospho-histidine in in vitro phenotypes including endocytosis, motility and proliferation.